There is known a pipe-tapered-thread machining tap for machining a pipe tapered internal thread in a pipe, a pipe adaptor, a fluid equipment or the like. In the pipe-tapered-thread machining tap, its complete thread portion as well as its chamfered portion is tapered for making the pipe tapered internal thread tapered, so that thread cutting is performed not only by the chamfered portion but also by the complete thread portion.
In the pipe-tapered-thread machining tap, the thread cutting performed by the complete thread portion is carried out not only by its crest but also by its root whereby larger cutting resistance is generated as compared with thread cutting performed by a chamfered portion in a pipe-straight-thread machining tap. Thus, in the pipe-tapered-thread machining tap, tap breakage, chipping, wear and other problems could easily occur, resulting in problems such as insufficiencies of machining efficiency and tool durability.
On the other hand, there is proposed a pipe-tapered-thread machining tap in which a total of edge thickness angles is 125°-150° for preventing breakage and chipping of the tap and also preventing cutting chip clogging so as to provide a high efficiency and a long tool life even where the tap is used for machining a high-hardness material. An example of such a pipe-tapered-thread machining tap is disclosed in Patent Document 1.